Reciprocating refrigeration compressor wrist pin retention

ABSTRACT

A compressor (20) has a case (22) and a crankshaft (38). The case has a number of cylinders (30 32). For each of the cylinders, the compressor includes a piston (34) mounted for reciprocal movement at least partially within the cylinder. A connecting rod (36) couples each piston to the crankshaft. A pin (44) couples each connecting rod to the associated piston. Each pin has first (52) and second (53) end portions mounted to first (56) and second (57) receiving portions of the associated piston and a central portion (48) engaging the associated connecting rod. For each of the pistons a pair of first and second at least partially non metallic plugs have respective stems received in the pin first and second end portions and respective heads facing a wall surface of the associated cylinder.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. Patent Application Ser. No. 61/696,724, filedSep. 4, 2012, and entitled “Reciprocating Refrigeration Compressor WristPin Retention”, the disclosure of which is incorporated by referenceherein in its entirety as if set forth at length.

BACKGROUND

The present disclosure relates to refrigeration compressors. Moreparticularly, it relates to reciprocating piston compressors utilized tocompress gases such as low global warming potential (GWP) and naturalrefrigerants.

A variety of refrigerant compressor configurations are in common use.Among these configurations are: screw compressors; scroll compressors;and reciprocating piston compressors. In a reciprocating compressor apiston head is driven between a lower position at which a fluid to becompressed enters the compression cylinder, and an upper or “top”position at which the compressed fluid is driven outwardly of thecylinder

An exemplary reciprocating piston compressor has a pin coupling eachpiston to the associated connecting rod. Such wrist pins may be in ajournaled rotating fit to one or both of the piston and rod. In oneexemplary configuration, a central portion of the pin is journaled in anend portion of the rod and end portions of the pin are journaled inassociated bores in the piston. The pin may be retained against axialmovement by clips abutting ends of the pins and partially captured inopen channels in the piston bores. Alternative retainers includepolymeric washers.

Separately, in the piston engine field, a proposal has been made to useplugs (U.S. Pat. Nos. 5,289,758 and 6,048,126) to position a wrist pin.In the compressor art, concealed plugs have been proposed in U.S. Pat.No. 5,850,777. Additionally plugs have been proposed in U.S. Pat. No.6,358,026.

SUMMARY

One aspect of the disclosure involves a compressor having a case and acrankshaft. The case has a number of cylinders. For each of thecylinders, the compressor includes a piston mounted for reciprocalmovement at least partially within the cylinder. A connecting rodcouples each piston to the crankshaft. A pin couples each connecting rodto the associated piston. Each pin has first and second end portionsmounted to first and second receiving portions of the associated pistonand a central portion engaging the associated connecting rod. For eachof the pistons a pair of first and second at least partiallynon-metallic plugs have respective stems received in the pin first andsecond end portions and respective heads facing a wall surface of theassociated cylinder.

In various implementations, an electric motor within the case may becoupled to the crankshaft. The plugs may comprise a non-metallicmaterial. They may comprise such material at least along the heads. Thematerial may be a polybutylene terephalate. The plugs may consist ofsuch material or consist essentially of such material. For each pin, therespective end portions may be journaled fit in the associated pistonreceiving portions. The central portion may be journaled fit in theassociated connecting rod. The pins may be axially retained by acooperation of the associated plug heads with the cylinder. They may beretained only via such cooperation. The plugs may comprise a pressurerelief channel along the stem. The pressure relief channel may extendalong an underside of the head. The heads may have a doubly convex outersurface having a principal radius of curvature within 5% of a transverseradius of curvature of the associated cylinder.

Other aspects of the disclosure involve a refrigeration system includingsuch a compressor. The refrigeration system may include a recirculatingflowpath through the compressor. A first heat exchanger may bepositioned along the flowpath downstream of the compressor. An expansiondevice may be positioned along the flowpath downstream of the first heatexchanger. A second heat exchanger may be positioned along the flowpathdownstream of the expansion device. The refrigerant charge may compriseat least 50% carbon dioxide or fluorocarbon by weight. The system may bea refrigerated transport system. The refrigerated transport system mayfurther comprise a container. The second heat exchanger may bepositioned to cool an interior of the container. The system may be afixed refrigeration system. The fixed refrigeration system may furthercomprise multiple refrigerated spaces. There may be a plurality of saidsecond heat exchangers, each being positioned to cool an associated suchrefrigerated space.

Another aspect of the disclosure involves a compressor wrist pinretaining plug comprising the unitarily molded combination of a hollowstem for receipt in a bore of a pin and a head. The stem protrudes froman underside of the head. A pressure relief channel is at leastpartially on the stem and head.

In various implementations, the channel may be an open channel extendingcontinuously along the stem and the underside of the head to a peripheryof the head. The stem may comprise a tapered end. The plug may comprisea polybutylene terepthalate. The plug may consist of polybutyleneterepthalate.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a compressor.

FIG. 2 is a vertical longitudinal sectional view of the compressor ofFIG. 1.

FIG. 3 is a partial vertical longitudinal sectional view of a cylinderof the compressor of FIG. 1.

FIG. 3A is an enlarged view of a wrist pin end of the cylinder of FIG.3.

FIG. 4 is a partial transverse longitudinal sectional view of thecylinder of FIG. 3, taken along line 4-4 of FIG. 3.

FIG. 5 is a view of a wrist pin plug for the compressor of FIG. 1.

FIG. 6 is an end view of the plug of FIG. 5.

FIG. 7 is a longitudinal/axial sectional view of the plug of FIG. 6,taken along line 7-7 of FIG. 6.

FIG. 8 is a partial radial inward view of a channel in the plug of FIG.6, taken along line 8-8 of FIG. 6.

FIG. 9 is a schematic view of a refrigeration system.

FIG. 10 is a schematic view of a fixed commercial refrigeration system.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIGS. 1 and 2 show an exemplary compressor 20. The compressor 20 has ahousing (case) assembly 22. The exemplary compressor includes anelectric motor 24 (FIG. 2). The exemplary case 22 has a suction port(inlet) 26 and a discharge port (outlet) 28. The housing defines aplurality of cylinders 30, 31, and 32. Each cylinder accommodates anassociated piston 34 mounted for reciprocal movement at least partiallywithin the cylinder. Exemplary multi-cylinder configurations include:in-line; V (vee); and horizontally opposed. The exemplary in-linecompressor includes three cylinders. Each of the cylinders includes asuction location and a discharge location. For example, the cylindersmay be coupled in parallel so that the suction location is shared/commonsuction plenum fed by the suction port 26 and the discharge location isa shared/common discharge plenum feeding the discharge port 28. In otherconfigurations, the cylinders may share suction locations/conditions buthave different discharge locations/conditions. In other configurations,the cylinders may be in series. An exemplary fluorocarbon-basedrefrigerant is R-410A. An exemplary carbon dioxide (CO₂)-based (e.g., atleast 50% CO₂ by mass/weight) refrigerant is R-744.

Each of the pistons 34 is coupled via an associated connecting rod 36 toa crankshaft 38. The exemplary crankshaft 38 is held within the case bybearings for rotation about an axis 500. The exemplary crankshaft iscoaxial with a rotor 40 and stator 42 of the motor 24. Each piston 30-32is coupled to its associated connecting rod 36 via an associated wristpin 44. FIG. 3 shows the pin 44 as having a central portion 46 mountedfor rotation in an aperture 48 in a distal end portion 50 of theconnecting rod 36. In various implementations, the aperture may be in abushing interference fit in a main piece of the connecting rod. The pinhas first and second end portions 52 and 53 mounted in apertures 54 and55 of associated receiving portions 56 and 57 of the piston (e.g., in anon-interference journaled fit).

The exemplary piston has a distal end face 60 and alateral/circumferential surface 62. One or more sealing rings 64 may becarried in corresponding grooves 66 in the surface 62. To seal with thecylinder lateral wall (bore) surface 70. In alternative cylinders, atleast a portion of the cylinder wall/surface 70 is formed by theinterior surface of a sleeve (e.g., press fit in the cylinder block 76).

As so far described, the compressor may be representative of any of anumber of possible reciprocating piston compressors to which thefollowing teachings may be applied.

FIG. 3 shows a pair of plugs 80 mounted in the associated pin endportions 52 and 53. Each of the plugs has a stem 81 (FIG. 3A) insertedinto end portions of a channel (e.g., a bore) 77 in the pin 59. The stem81 depends from the underside 82 of a head 83. The head undersides abutpin ends (rims) 78 and 79. As is discussed further below, the heads havea doubly convex outer surface 84. Exemplary head outer surfaces 84 arein close facing relation or contacting the cylinder wall 70. Theexemplary curvature is such that, as seen in the transverse sectionalview of FIG. 4, the surface 84 along a transverse centerplane 522 (FIG.6) is concentric with the cylinder wall (FIG. 4). Exemplary plug headsare rotationally symmetric about the axis 520 except for the channel 100and thus have similar curvatures along the transverse centerplane 522and vertical centerplane 524. It is noted that the plugs need not belimited to this orientation. Additionally, other channel configurationsmay be featured as may other stem and head configurations. The exemplaryconfiguration matches head radius of curvature R_(CP) to within 10%(more narrowly, 5%) with the transverse radius of curvature R_(CC) ofthe cylinder wall surface along a majority of a circumferential lengthof the head along such transverse plane (R_(CP) thus typically beinglower than R_(CC). Overall axial (relative to the pin axis but diametricfor the cylinder) clearance is twice the illustrated centered clearanceΔR. The float of the pin may close the gap at either end. Wear of thehead may expand the clearance. Exemplary combined clearance at the headsof the two plugs is 3-6 mm, more particularly 4.0-5.5 mm or 4.1-5.4 mmwhen new. With a cylinder inner diameter (ID) of about 62.1 mm, anexemplary wrist pin length is 54.6 mm or at least 85% thereof, moreparticularly 85-92% or 87-90%.

FIG. 5 shows further details of the exemplary plug 80. The stem 81extends to a distal end 85. In the exemplary embodiment, the end 85 isformed as a rim surrounding a central compartment/channel 86. Theexemplary compartment 86 extends along a central axis 520 (FIG. 6) tothe head or near the head. FIG. 7 shows the exemplary compartmentdefined by a surface comprising a tapering surface 88 (at an exemplaryconstant half angle θ₁) extending inward from the rim 85 to a nearlysemi-spherical surface 89 forming a base/end of the compartment. FIG. 7also shows a stem length L_(S) from an intact (discussed later) planarportion of the head underside 82 to the rim 85. FIG. 7 also shows acompartment depth D_(C) which may be very close to or coincident toL_(S). In terms of additional dimensions, FIG. 7 shows the head ashaving an approximately cylindrical peripheral/lateral surface 90 havinga diameter D_(H). A height of the head is shown as L_(H). In thisembodiment, exemplary D_(H) is 21 mm, more broadly 19-22 mm. Other sizeswould be appropriate for other compressors. Similarly, exemplary L_(S)from is 7 mm, more broadly 5-10 mm. Exemplary stem diameter is 10 mm,more particularly about 9.6 mm

Returning to FIG. 5, the exemplary stem is shown as having a variedcross-section or diameter. Proximally of the rim 85 is a frustoconicalbevel 92. The exemplary bevel 92 has a length L_(B) (FIG. 7) and a halfangle θ₂ and a length L_(B). Proximally of the surface portion 92 is ashallower main surface portion 94 (e.g., frustoconical) extending over alength L_(M) at a half angle θ₃. A generally cylindrical surface portion96 extends proximally of the surface portion 94 and along with aradiused transition 97 (at a stem root 98) to the head underside extendsfor a length L_(R). Head height L_(H) and perimeter height L_(P) areadvantageously low enough to allow sufficient length of engagementbetween pin and piston, but advantageously thick enough to provide wearresistance and ease of molding. Exemplary D_(H) is slightly lower thanthe wrist pin diameter D_(P) (e.g., 90-100%, more particularly 92-99% or93-98%). Exemplary L_(P) are 1-3 mm, more particularly, 1.0-2.0 mm. Withthe exemplary cylinder diameter of 62 mm and 31 mm radius, exemplaryprincipal head radius of curvature is within 10% or 5% of this as notedabove, more particularly 95-100% (29-31 mm for this example).

As is discussed further below, the plug includes a pressure reliefchannel 100 (FIG. 5). The exemplary pressure relief channel includes afirst portion 102 along or through the stem and a second portion 104along or through the head. The exemplary channel is open along boththese portions 102 and 104. The portion 102 extends from a distal end106 to a proximal end at a junction with the portion 104 at the stemroot. The portion 104 extends radially outward along the head underside82 to a second end 108. FIG. 6 shows the channel as including a firstrim 110 and a second rim 112 with a base 114 therebetween. Exemplarychannel depth D_(C) along the stem is nominal 1.3 mm, with a +/−0.5 mmtolerance. More broadly, exemplary depth is 0.5-2.0 mm. Exemplary depthalong the head underside may be smaller (due to less deformation; thestem is subject to a deforming press-fit, whereas the head has lesscontact force). Exemplary depth along the head is at least 0.05 mm, moreparticularly 0.05-0.02 mm. Exemplary width W_(C) is greater than thedepth along the stem (e.g., about twice, more broadly 1.5-3.0 times or2.6+/−0.5 mm in this example). The exemplary channel is arcuate incross-section (e.g. of an essentially constant radius of curvature).

Exemplary plugs are entirely or at least along outboard portions thereofpolymeric/resinous. Exemplary polyester resin is a semi-crystallinepolybutylene terepthalate (PBT) such as VALOX 310 from SABIC InnovativePlastics Holding BV, Riyadh, Saudi Arabia. Exemplary such plugs areinjection molded.

In the installed condition, the pin bore 59 surface and associated pinrim laterally enclose the channel 100 to allow venting between the pininterior and the associated space between the head and cylinder wall.This resists any tendency of any excess of pressure in the pin drivingthe plugs outward into contact with the cylinder wall which wouldencourage wear of the head.

FIG. 9 shows an exemplary refrigeration system 140 including thecompressor 20. The system 120 includes a system suctionlocation/condition 150 at the suction port 26. A refrigerant primaryflowpath 152 proceeds downstream from the suction location/condition 150through the compressor cylinders in parallel to be discharged from adischarge location/condition 154 at the discharge port 28. The primaryflowpath 152 proceeds downstream through the inlet of a first heatexchanger (gas cooler/condenser) 156 to exit the outlet of the gascooler/condenser. The primary flowpath 152 then proceeds downstreamthrough an expansion device 162. The primary flowpath 152 then proceedsdownstream through a second heat exchanger (evaporator) 164 to return tothe suction condition/location 150.

In a normal operating condition, a recirculating flow of refrigerantpasses along the primary flowpath 152, being compressed in thecylinders. The compressed refrigerant is cooled in the gascooler/condenser 156, expanded in the expansion device 162, and thenheated in the evaporator 164. In an exemplary implementation, the gascooler/condenser 156 and evaporator 164 are refrigerant-air heatexchangers with associated fan (170; 172)—forced airflows (174; 176).The evaporator 164 may be in the refrigerated space or its airflow maypass through the refrigerated space. Similarly, the gas cooler/condenser156 or its airflow may be external to the refrigerated space.

Additional system components and further system variations are possible(e.g., multi-zone/evaporator configurations, economized configurations,and the like). Exemplary systems include refrigerated transport unitsand fixed commercial refrigeration systems.

An exemplary fixed commercial refrigeration system 250 (FIG. 10)includes one or more central compressors 20 and heat rejection heatexchangers 156 (e.g., outside/on a building 255) commonly servingmultiple refrigerated spaces 256 (e.g., of retail display cabinets 258in the building). Each such refrigerated space may have its own heatabsorption heat exchanger 164′ and expansion device 162′ (or there maybe a common expansion device). Other rack-mount situations includebuilding heating, ventilation and air conditioning (HVAC).

The compressor may be manufactured via otherwise conventionalmanufacturing techniques. The pistons, pins, rods, and cylinder blockmay be cast and/or machined as may other components. The assembly mayinvolve mounting the connecting rods to the pistons via the pins. Thismay be performed by hand. Similarly, the plugs may be installed by handwith the surface portion 92 of FIG. 5 guiding insertion into the pinbore. This may eliminate the use of press-fitting or clip-applying toolsin a baseline compressor. The pistons may be inserted into thecylinders. The connecting rods may be mated to the crankshaft. The casemay be assembled over the crankshaft (e.g., by mating a sump to thecylinder block). The remaining elements may be assembled.

Although an embodiment is described above in detail, such description isnot intended for limiting the scope of the present disclosure. It willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. For example, whenimplemented in the reengineering of an existing (baseline) compressorconfiguration, details of the existing configuration may influence ordictate details of any particular implementation. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A compressor (20) comprising: a case (22) havinga plurality of cylinders (30-32); a crankshaft (38); and for each ofsaid cylinders: a piston (34) mounted for reciprocal movement at leastpartially within the cylinder; a connecting rod (36) coupling the pistonto the crankshaft; and a pin (44) coupling the connecting rod to thepiston, the pin having: first (52) and second (53) end portions mountedin first (56) and second (57) receiving portions of the piston; and acentral portion (48) engaging the connecting rod, wherein: a pair offirst and second at least partially non-metallic plugs (80) comprising apolybutylene terepthalate have respective stems (81) received in the pinfirst and second end portions and respective heads (83) each having asurface (84) facing a wall surface (70) of the associated cylinder; theplugs comprise a pressure relief channel (100) along the stem; and thepressure relief channel extends along the entire radial span of anunderside of the head from the stem to a lateral periphery of the headat the outer diameter (90) of the head.
 2. The compressor of claim 1further comprising: an electric motor (24) within the case coupled tothe crankshaft.
 3. The compressor of claim 1 wherein: the polybutyleneterephthalate is semi-crystalline.
 4. The compressor of claim 1 wherein:the pin has an interior; and the channel cooperates with the pin toallow venting between the pin interior and an associated space betweenthe head and a wall of the cylinder wall.
 5. The compressor of claim 1wherein: the plugs consist of non-metallic material.
 6. The compressorof claim 1 wherein: for each said pin, the respective end portions arejournaled fit in the associated piston receiving portions.
 7. Thecompressor of claim 6 wherein: for each said pin, the central portion isjournaled fit in the associated connecting rod.
 8. The compressor ofclaim 7 wherein: the pins are axially retained only via cooperation ofthe associated plug heads with the cylinder.
 9. The compressor of claim1 wherein: the pressure relief channel (100) is an open channel alongthe stem.
 10. The compressor of claim 9 wherein: the pressure reliefchannel extends as said open channel along an underside of the head. 11.The compressor of claim 1 wherein: the heads have a doubly convex outersurface having a principal radius of curvature within 5% of a transverseradius of curvature of the associated cylinder.
 12. A refrigerationsystem (140; 250) comprising: the compressor (20) of claim 1; arefrigerant recirculating flowpath (152) through the compressor; a firstheat exchanger (156) along the flowpath downstream of the compressor; anexpansion device (162; 162′) along the flowpath downstream of the firstheat exchanger; and a second heat exchanger (164; 164′) along theflowpath downstream of the expansion device.
 13. The refrigerationsystem of claim 12 wherein: a refrigerant charge comprises at leastabout 50% carbon dioxide or fluorocarbon by weight.
 14. The system ofclaim 12 being a fixed refrigeration system further comprising: multiplerefrigerated spaces (256); and a plurality of said second heatexchangers (164′), each being positioned to cool an associated saidrefrigerated space.
 15. A compressor wrist pin retaining plugcomprising: a unitarily molded combination of a hollow stem for receiptin a bore of a compressor wrist pin and a head, the stem protruding froman underside of the head; and a pressure relief channel being an openchannel extending continuously along the stem and the underside of thehead to a lateral periphery of the head at the outer diameter of thehead, the head having a doubly convex outer surface.
 16. The plug ofclaim 15 wherein: the stem comprises a tapered end.
 17. The plug ofclaim 15 comprising: a polybutylene terepthalate.
 18. The plug of claim15 consisting of: a polybutylene terepthalate.
 19. A compressor (20)comprising: a plurality of compressor wrist pin retaining plugs (80) ofclaim 15 and: a case (22) having a plurality of cylinders (30-32); acrankshaft (38); and for each of said cylinders: a piston (34) mountedfor reciprocal movement at least partially within the cylinder; aconnecting rod (36) coupling the piston to the crankshaft; a pin (44)coupling the connecting rod to the piston, the pin having: first (52)and second (53) end portions mounted in first (56) and second (57)receiving portions of the piston; and a central portion (48) engagingthe connecting rod; and a pair of first and second said compressor wristpin retaining plugs (80) with their respective hollow stems (81)received in the pin first and second end portions and their respectiveheads (83) each having a surface (84) facing a wall surface (70) of theassociated cylinder.
 20. A compressor wrist pin retaining plug (80)comprising: the unitarily molded polybutylene terepthalate combinationof a hollow stem (81) for receipt in a bore of a pin and a head (83),the stem protruding from an underside (82) of the head; and a pressurerelief channel (100) at least partially on the stem and the head andextending along the entire radial span of an underside of the head fromthe stem to a lateral periphery of the head at the outer diameter (90)of the head so as to provide venting of an interior of a pin when theplug stem is received in the bore of the pin and a rim of the pincontacts the underside of the head.
 21. The compressor wrist pinretaining plug (80) of claim 20 wherein: the stem has a compartmentextending from a rim of the stem to a base.